Composite materials in brought terms are known from the state of the art, such as for example from international application WO-01/02165. In such a composite material the core material (which determines by far the largest component of the composite material) mainly determines the bulk mechanical properties of the composite material, such as for example the strength thereof. The clad sheet however (which, consequently, only determines a small fraction of the composite material and thus will be of minor importance for the mechanical properties thereof) is in contact with the environment surrounding the composite material and thus will determine the chemical activity, for example to a very large extent the corrosion performance of the composite material.
As examples of aluminium composite materials according to the state of the art firstly brazing sheet having typically an aluminium alloy from the AA3xxx-series as core material (e.g. AA3003) and on one or both sides thereof an aluminium alloy from the AA4xxx-series (e.g. AA4045 or AA4343) as clad sheet, as well as sheets for aeronautical use (core material comprising an aluminium alloy from the AA2xxx-series and clad sheet typically comprising an aluminium alloy from the AA1000-series) such as Alclad 2024-1230 may be mentioned. It is common for such known composite materials that these are developed for a specific use and for fulfilling specific demands.
International patent application WO-00/26020 discloses a composite aluminium panel of two parallel sheets or plates secured to the peaks and troughs of a corrugated aluminium stiffener sheet. The corrugated aluminium stiffener sheet is made from an AlMgMn alloy and having 0.4-5.0% Zn. It is disclosed that the corrugated aluminium sheet has a very good corrosion resistance. However, in certain extreme corrosive environment it may be useful to provide a cladding which further enhances to the corrosion resistance of the alloy product. Such a cladding can be of an AA1000-type alloy, an AA6000-type alloy having more than 1% of alloying additions, and an AA7000-type alloy having more than 0.8% of Zn such as AA7072.
International application WO-98/24571 discloses a multilayer metal composite product obtained by compound strand casting. The product comprises a core, preferably an aluminium alloy, on at least one side of the core an interlayer bonded to the core and a cladding bonded to the interlayer. Depending on the application of the product, the cladding forming the outersurface of the composite product can be a aluminium brazing alloy for use in brazing sheet, an AA1xxx-series alloy to obtain a mirror like surface finish, or an zinc containing aluminium alloy or zinc or a zinc alloy to improve corrosion resistance.
As will be appreciated herein below, except as otherwise indicated, all aluminium alloy designations refer to the Aluminum Association designations in Aluminium Standards and Data and the Registration Records, as published by the Aluminium Association in 2006.
For this invention “sheet product” refers to a rolled product form over 0.15 mm through 2.5 mm in thickness with sheared, slit, or sawed edges.
For this invention “automotive body sheet” or “ABS” refers to aluminium alloy sheet for automotive body applications, in particular exterior panels, interior panels and structural parts.
For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.